This is a guide on the various Sion item builds, rune builds, and matchups that you will see in top lane. Sion is a tank, many assume that he is an extremely good late game tank as his W passive will give him theoretically infinite health so long as he is killing things. This is false. Sion peaks in power in the mid game with around 3 items. He is an extremely strong skirmisher, along with good peel and cc. He is primarily used as a tank, although AD Sion is also quite good at being an extremely strong side laner. When going AD Sion , you are primarily looking to play for towers and disrupting the side lanes rather then team fighting. Sion as a champion also experiences a lot of counters. Many champs counter him extremely har, leading to a lot of hard matchups. Some matchups can be better though if you choose to go AD vs tank. Proxying is also a heavily used technique in order to avoid many of the bad lane matchups that are truly unplayable. In most matchups that are not unplayable you can be defined as a lane bully, with your high damage burst.

Q- Decimating smash - Heavy damage ability that can be charged for up to two seconds, after one second of charging you will knock up your enemy and stun them for 1.25 to 2.25 seconds based on charge time. This is your bread and butter damage ability in lane. It is extremely important to space yourself accordingly with this ability so they have to choose whether to walk to you or walk away, so you can gurantee hits with as much charge time as possible.
W- Soul furnace - Creates a shield that you can recast if still alive after 3 seconds that will detonate dealing magic damage around you. This shield is extremly good for damage and poke. It deals an extra 14% health max health magic damage. It also has a passive effect that will give you an extra 4 health per cs kill, and 15 for champion takedowns, cannon minions, and large monsters.
E- Roar Of The Slayer - shoots out a shockwave that when enemies are hit, deals a small amount of damage, slows, and reduces their armor by 20% for 4 seconds. This is an ability that is used to increase the total damage of things like your Q or ult. When an enemy laner looks to take a minion, i like to try and E them so i can increase my q damage and punish them better, this also slows them and makes my q easier to hit.
R- Unstoppable Onslaught - Sion charges unstoppably in a direction for 8 seconds, at the end of the charge sion deals a large amount based of distance traveled. Any champion he hits are stunned between 0.75 seconds and 1.75 seconds bsaed on distance traveled, enemies farther out and still hit with his radius damage are slowed for 3 seconds . This ability ends with the collision of an enemy or a wall. This ability is extremely strong for sion. This allows you to flank enemies extremely well, and do tons of damage. His ult is also great for escaping situations as you rapidly gain MS and are only stopped by someone getting infront of you. This ability can also be used in order to get back to lane and not miss any minions. Its a extremely utility based ult that can be used for your need. It also deals damage to towers if you hit them or end your ult blast next to it.